#include <iostream>
using namespace std;

const int kMaxN = 2e5 + 10;

bool vis[kMaxN];

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int x;

    cin >> x;
    vis[x] = true;
  }
  for (int i = 1; i <= n; i++) {
    if (vis[i] == false) {
      cout << i << "\n";
      break;
    }
  }
  return 0;
}